It is often desirable to be able to determine the distance to a surface or to an object without there being physical contact with the object. For example, in my co-pending application Ser. No. 675,665, Filed Nov. 28, 1984, I describe a surface position sensor in which a beam of energy is directed toward a surface at a predetermined angle so that light is focused at a point on the surface when the surface is in the middle or center position of its extremes. Reflected light is received by an optical system located at a similar angle from the projection system but on opposite sides thereof and energy that is reflected parallel to the optic axis passes through an aperture so as to reach a detector at a position which is indicative of the position of the surface. The detector used in this application was referred to as a "lateral effect photo-diode" detector which is temperature sensitive and in some cases rather unpredictable.
In my co-pending application Ser. No. 826,057, Filed Feb. 4, 1986, and now abandoned, I describe a radiation position sensor comprising an elongated piece of material which could receive radiation from the reflected surface and diffuse or scatter such radiation within itself. The material was surrounded by a layer of material having a reflective interior surface and as the beam of radiation entered the tube through a window it would diffuse out towards either end in an amount which varied with the distance from the entrace point to the ends. Normal photo-diodes were mounted at each end and it was found that the effects of temperature were less pronounced and more repeatable possibly because the material scattered the light to the normal photo-diodes rather than causing electron migration as was the case with the latteral effect photo-diodes.